Process and Apparatus for Generating and Delivering an Enriched Gas Fraction

ABSTRACT

An improved sieve bed design to manage breakthrough and the mass transfer zone by way of volumetric division. An empty space in the product end is separated from adsorbent-filled sieve space in the feed end by a mid-diffuser plate. The ratio of the empty product end void space to the adsorbent filled sieve space within a sieve bed may be determined by the relative percentages of the gasses to be separated and the bulk loading factor of the molecular sieve. In operation, pressure in the sieve bed empty space and sieve filled space may be equal at any instant. This contains breakthrough to the location of the mid-diffuser plate. The mass transfer zone may be static at the point of the mid-diffuser plate and as such, gas separation is a function of pressure within the bed.

FIELD OF THE INVENTION

This invention relates to the field of gas concentrators and gasconserving devices.

BACKGROUND OF THE INVENTION

The process of pressure swing adsorption (PSA) to enrich theconcentration of a gas, such as the oxygen concentration, is known inthe prior art. The challenge has been to generate sufficient quantitiesor flow rates of the enriched gas, in a sufficiently high concentration,to enable the therapeutic use of a PSA machine. A further challenge hasbeen to make such a machine portable, that is relatively small andlightweight, self-sufficient, and self contained for realisticportability by a patient over an extended period of time.

It is also known in the prior art to attempt to conserve the target gasusing an oxygen conserving device (OCD), that is, conserve the use offor example high concentration oxygen by a patient so as to pro-long thesupply of the target gas from. Thus in one aspect of the presentinvention, it may be advantageous to combine a target gas concentrator,for example, an oxygen concentrator, with an OCD to enhance the durationof supply of the enriched gas from the gas concentrator, therebyenhancing the self sufficiency of both the device and patient.

As known in the prior art, oxygen is prescribed for patients sufferingfrom chronic obstructive pulmonary disorder (COPD). By way ofbackground, the practice of providing oxygen to COPD patients is knownas long-term oxygen therapy (LTOT). The oxygen cylinders conventionallyprovided to patients for therapeutic use are typically large and heavy.Smaller, lighter cylinders are available but have a limited duration ofoxygen flow.

Oxygen conserving devices were introduced which enabled cylinders todeliver sufficient oxygen for greater periods of time by only providingoxygen when the patient would inspire. In those devices, a fixed volumeof oxygen is delivered, at a high flow rate, to the patient upondetection of inspiration. The volume of oxygen delivered per breath tothe patient, per setting, is claimed to produce the same blood oxygenconcentration in the patient as a continuous flow device at the samesetting.

An oxygen-conserving ratio can be defined based on the volume deliveredto the patient by a continuous flow oxygen system, at any given setting,compared to the volume delivered by the OCD. There are two common fixedratios, 3:1 and 6:1. A doctor may find that a particular patient at restwill have sufficiently high blood oxygen concentration for a given pulsedose as metered by the OCD at a particular setting. However, if thepatients' oxygenation requirements increase as a consequence of physicalactivity, increasing the amount of oxygen metered based on a fixed ratiopulse dose may not be effective. It could be that the patient requiresmore oxygen than the conserving device will supply to maintain bloodoxygenation. To compensate for this a doctor may choose to prescribe thehighest setting. This of course would then not be the most efficient useof oxygen.

The patient inspiration is detected by the OCD when a partial vacuum isproduced in the nasal cannula. If breathing occurs partially through themouth, such as when a patient is sleeping, the vacuum in the nasalcavity may be too shallow to be detected by the sensor. Increasing thesensitivity of the sensor introduces a new problem of possible falseinspiration detection whenever the cannula is bumped, as a result of thedifferential pressure created within the cannula as it shakes.

In the field of gas concentrators it is known to use zeolite to adsorbnitrogen in an oxygen concentrator. The use of zeolite herein isintended to be exemplary. It would be known to one skilled in the art totailor the use of a specific adsorbent, whether a particular type ofzeolite or other adsorbent. As is known in the prior art, zeoliteconsists of molecular sized polyhedral cages. Oxygen and nitrogenmolecules (for example) can access the inside of these cages throughholes in the crystalline structure. The crystalline structure containscations. Gas adsorption occurs when molecules are attached to thesecations through electrostatic forces. Nitrogen molecules bind strongerto the zeolite cations than oxygen molecules. As a result, if a mixtureof nitrogen and oxygen, such as found in atmospheric air, is pressurizedinto a chamber full of zeolite particles, nitrogen will adsorb into thezeolite particles more readily than oxygen. There will be a higherconcentration of oxygen in the empty space between the zeoliteparticles, (hereinafter referred to as zeolite void space), than therewas in the original gas mixture.

A conventional pressure swing adsorption gas separation cycle in anoxygen concentrator works as follows:

-   -   (a) A first cylindrical zeolite filled chamber is pressurized        from the feed end with atmospheric air, while oxygen enriched        gas exits from the product end through a gas flow restrictor.    -   (b) The oxygen enriched gas flow passes through a conduit        junction. A portion of the oxygen-enriched gas is delivered for        end use. The remaining portion of the oxygen-enriched gas        travels through the product end of a second cylindrical zeolite        chamber and is vented to atmosphere from a vent located at the        feed end of the chamber. This gas flow is counter current to the        direction of pressurization of the second chamber, (hereinafter        referred to as counter flow), to push nitrogen out of the second        chamber.    -   (c) The second zeolite filled chamber is pressurized from the        feed end with atmospheric air, while oxygen enriched gas exits        from the product end through a gas flow restrictor.    -   (d) The oxygen enriched gas flow passes through the conduit        junction. A portion of the oxygen-enriched gas is delivered for        end use. The remaining portion of the oxygen enriched gas        travels through the product end of the first chamber and is        vented to atmosphere from a vent located at the feed end of the        chamber. This gas flow is counter current to the direction of        pressurization of the first chamber to push nitrogen out of the        first chamber.

The cycle is then repeated.

During oxygen enriched gas generation nitrogen is left adsorbed into thezeolite particle structure. A conventional approach to removing thenitrogen from the chamber is to blow oxygen enriched gas across thezeolite from the product end of the chamber to the feed end of thechamber. This counter-flow pushes nitrogen gas, as a wave, to the feedend of the zeolite chamber and out the vent to the atmosphere. Sincenitrogen is strongly bound to the zeolite cations, it takes a largequantity of oxygen enriched gas flow in conjunction withdepressurization to remove it. Another method to remove the nitrogenfrom the zeolite chamber is to evacuate the chamber with a vacuum pump.

Conventional PSA sieve bed design thus provides for the flow of gasthrough a sieve bed from the inlet or feed end to the outlet or productend. The sieve beds are completely filled with molecular sieve. Acalibrated orifice at the product end provides resistance to the flow ofgas through the sieve bed. This resistance to flow provides thenecessary pressurization of the sieve bed to facilitate nitrogenadsorption by the molecular sieve. The bed is pressurized for a periodof time, which corresponds to the propagation of the mass transfer zonethrough the bed. The mass transfer zone is a build up of nitrogen, whichmoves as a front from the feed end of the bed to the product end of thebed. The mass transfer zone moves as a consequence of gas flow throughthe bed, but may propagate independently of the gas flow. The point atwhich the mass transfer zone reaches the outlet (product end), where anyfurther pressurization will result in high concentrations of nitrogenleaving the product end, is referred to as “breakthrough”.

By way of analogy, when humid air is introduced into one end of a drydesiccant filled cylinder, the desiccant incrementally soaks up thewater vapor in the air. As a result, the gas that has passed through thedesiccant bed is dryer than the gas that entered it. Water is adsorbedfirst by the first available desiccant particles that appear in the flowstream. Thus the desiccant near the entrance of the desiccant filledcylinder will be filled with water vapor well before the desiccant nearthe exit of the cylinder. As the total volume of humid air that haspassed through the desiccant increases, the volume of the desiccantfilled with water increases from the feed end of the cylinder to theexit of the cylinder. Eventually the desiccant that is near the exit ofthe cylinder is filled with water as well. At this point, no more watervapor can be adsorbed. If more water vapor is added after this point,the water vapor will just pass straight through the desiccant filledcylinder. This is an example of “breakthrough”. Likewise, for any givenpressure, a molecular sieve material such as zeolite can only adsorb afinite volume of nitrogen before breakthrough occurs.

Although applicants do not wish to be held to any particular theory ofoperation of a device according to the present invention, in applicant'sopinion in considering the adsorption performance of a sieve bed design,there may be several key dynamics which function interdependent of eachother. The critical performance parameters (excluding the bed designitself and related flow dynamics) may be: working pressure of the bed,rate to pressurization, restrictive orifice size, duration ofpressurization, flow rate through the sieve bed and molecular sieveperformance. If any one of these parameters in a current sieve beddesign is changed without adjusting the others, the propagation of themass transfer zone or breakthrough may be affected.

For instance: If the rate to pressurization is too slow, diffusion mayoccur in the bed and concentration purity may not be reached. If therate to pressurization is too fast, “jetting” may occur and cause shadowzones (inactive areas in the sieve bed), early breakthrough, andcompromise concentration purity. If the orifice size is wrong, all flowdynamics may be affected which may result in diffusion or earlybreakthrough. If the duration of pressurization is too short the bed maynot be as efficient as it was designed to be and produce less gas. Ifthe duration of pressurization is too long, breakthrough may occur andcompromise concentration purity. If the flow rate through the sieve bedis too fast, diffusion of the mass transfer zone or early breakthroughmay occur. If the flow rate through the sieve bed is too slow diffusionof the mass transfer zone could occur. If the bulk-loading ratiochanges, that is, if the potential for quantity of gas to be adsorbed bythe molecular sieve changes, concentration purity may be affected. Ifthe adsorbent selectivity changes, that is, if the preference for thetarget gas to be adsorbed over the product gas by the molecular sievechanges, concentration purity may be affected.

PRIOR ART

Many industrial processes require purified gases. Such gases are used asreactants to produce other products by techniques called synthesis,i.e., formation of a compound from simpler compounds or elements.Particularly in cases where high purity gases are required, adsorptionis used as the separation technique. In particular, pressure swingadsorption (PSA) is frequently used because it is relatively simple,fast, and economical, in addition to having the capability of producingvery pure products. The use of PSA is especially prevalent in relativelysmall sized operations for which the use of a cryogenic separation plantis not economical. This has been on account of the economy of scale ofcryogenic plants, which are impractical below capacities of about 6,000scfm (standard cubic feet per minute) or 10,000 Nm³/h (normal cubicmeters per hour).

Most PSA systems produce a single purified gas stream, often the lessstrongly adsorbed (or light) component, from a given feed mixture. Inthese systems, the feed gas is passed through an adsorbent bed at a highpressure. In a sequence of steps, called the PSA cycle, this step isreferred to as the feed step. The adsorbent, by definition, is capableof selectively adsorbing the more strongly adsorbed (or heavy)component. Hence, the light component passes through the bed and iscollected as the purified product. Subsequently, the heavy component isdesorbed from the adsorbent, by opening an exhaust valve and allowinggas to escape until a low pressure is reached, which is called theblowdown step. This stream is frequently a by-product or waste.Alternatively, PSA systems can be designed to operate somewhatdifferently when the desired primary product is the heavy component. Forexample, Reinhold et al. in U.S. Pat. No. 5,536,300 (1996) disclose ameans by which a natural gas feed stream, containing significantquantities of nitrogen can be increased to a content of greater than 95%by volume of methane. In such systems, a rinse step follows the feedstep, in which the residual interstitial feed gas is displaced throughthe bed, for the purpose of recycling it, by introducing product gas. Ahigh purity heavy product is collected by blowdown, and/or evacuation(i.e., depressurization to subatmospheric pressure) and purge steps.

Normally, a low-pressure step follows blowdown or evacuation, called thepurge step, in which the light gas is admitted to the adsorbent bed, todrive off some or all of the residual heavy component. Finally, theadsorbent bed is repressurized in order to commence the subsequent feedstep, as mentioned at the beginning of this paragraph. Usually, only asingle component of the feed mixture is captured as either the light orheavy product, while the remaining components are exhausted from thesystem as waste. However, in some cases both the light and heavyproducts can be captured, e.g., as disclosed by Knaebel in U.S. Pat. No.5,032,150 (1991).

U.S. Pat. No. 4,013,429 by Sircar and Zondlo discloses a PSA process inwhich air is passed first through a pretreatment adsorber to removemoisture and carbon dioxide. The purified air then is passed through anadsorbent bed in which nitrogen is the more strongly adsorbed component.The oxygen-rich product is collected in an expandable receiving vessel.Following the feed step, the main bed is rinsed with high puritynitrogen product gas from a previous stage in the operation. High puritynitrogen is subsequently desorbed by blowdown and evacuation from themain bed. Following evacuation, the beds are repressurized with aportion of the oxygen-rich gas drawn from the expandable receivingvessel. The process of this system is complicated, having sixteen cyclesteps, thirteen valves, at least two compressors and one vacuum pump,and at least two expandable gas receivers. It mentions no enhancement ofperformance based on the volume or size of the expandable gas receiversrelative to that of the adsorbent.

U.S. Pat. No. 4,892,565 by Schmidt et al. (1990) reveals a process forrecovery of a heavy (more strongly adsorbed) key component from a gasmixture containing the key component and one or more light (lessstrongly adsorbed) secondary components using sub atmospheric PSA,sometimes called vacuum swing adsorption (VSA or VPSA). The processreduces or eliminates gas storage vessels and reduces power requirementsby operating without a feed compressor. Thus, feed is introduced undervacuum, achieved by pressure equalization between parallel adsorptionbeds, and due to the presence of a vacuum train for the heavy product.The elimination of product receivers is purely economical, since itmentions no enhancement of performance based on the absence of suchreceivers.

Several patents disclose the presence of a cavity or reservoir that isused to retain purge gas (e.g., U.S. Pat. Nos. 3,464,186; 4,487,617; and5,715,621). Those patents are related to PSA separation of moisture fromair. U.S. Pat. No. 3,464,186 issued to Hankison (1969) refers to thereservoir as a purge chamber and as the upper plenum. It mentions noenhancement of performance based on its volume or size relative to thatof the adsorbent. U.S. Pat. No. 4,487,617 by Dienes et al. (1984) refersto the reservoir as a gas-receiving cavity. It teaches nothing withrespect to enhancement of performance based on the volume or size ofthat cavity relative to that of the adsorbent. U.S. Pat. No. 5,715,621by Mitsch (1998) refers to the reservoir as a canister bore implyingthat it is mainly large enough to hold the adsorbent canister, but itteaches nothing with respect to performance enhancement based withrespect to its volume relative to that of the adsorbent-filled canister.

Some other patents happen to show reservoirs or cavities, but as aconsequence of being intended for radial flow (through an annular bed ofadsorbent). For example, U.S. Pat. Nos. 4,863,497; 5,232,479; and5,759,242, all show adsorbent occupying a portion of the vessel, andempty volume in the remainder. None of those teach anything with respectto enhancement of performance based on the volume or size of the emptyvolume relative to that of the adsorbent. For example, U.S. Pat. No.4,863,497 describes splitting that volume into partitions, but mentionsnothing about its capacity or size. Similarly, U.S. Pat. No. 5,232,479says, “It is an object of the present invention to propose an adsorberof compact design, . . . , which . . . limit the dead volumes of gasand, consequently, the losses of charge during operation, and thereforeenable a substantially improved productivity.” Consequently, ifanything, it teaches that excess volume is to be avoided. Claim 14 ofU.S. Pat. No. 5,759,242 says, “The vessel as recited in claim 1, whereinvoid volume within said gas feed channel and said gas feed inlet meansis in a range of 10%-25% of volume of said annular adsorbent bed.”;while Claim 15 says, “The vessel as recited in claim 14, wherein voidvolume within said product flow channel and said product outlet means isin a range of 3%-10% of volume of said annular adsorbent bed.” It goeson to say, “Accordingly, it is an object of the invention to provide animproved vessel for use in a VPSA or PSA process which employs only asingle adsorber chamber with low void volumes.” Thus, by indicating thatproduct-end void volume should be very small, this patent associates itwith inferior performance.

Contrary to the PSA separation processes disclosed in the prior art, thepremise of the present invention is that product end void volume, whencorrectly sized can be beneficial to the operation of a PSA system, byreducing the necessary power and by improving performance through themaintenance of plug flow during the purge step of the PSA cycle. Thepresent invention, then, provides a PSA process and system capable ofminimizing the power consumption, and operating cost of recovering apurified product from a feed gas mixture.

SUMMARY OF THE INVENTION

Thus, it is one object of the present invention to provide a gasconcentrator, which is less prone than prior PSA devices to diffusion,breakthrough, or jetting. It is also an object of the present inventionto generate oxygen-enriched gas utilizing a plurality of zeolitechambers using a more energy efficient method than previously used inprior art. The improved sieve bed design according to the presentinvention physically manages both breakthrough and the mass transferzone by way of volumetric division. An empty space in the product end isseparated from adsorbent-filled sieve space in the feed end by amid-diffuser plate. The ratio of the empty product end void space to theadsorbent filled sieve space within a sieve bed is determined by therelative percentages of the gasses to be separated and the bulk loadingfactor of the molecular sieve. A product end void space of the correctvolume may ensure the maximum volume of nitrogen has been adsorbedbefore breakthrough occurs. This is because the product end void spacevolume establishes the flow of gas through the molecular sieve. Inoperation, pressure in both sides of the sieve bed (empty space andsieve filled space) is equal at any instant. This contains breakthroughto the location of the mid-diffuser plate. Also, the mass transfer zoneis static at the point of the mid-diffuser plate and as such, gasseparation is simply a function of pressure within the bed.

The bed is, thus, unaffected by the rate of pressurization. Theoperating pressure is infinitely variable within the working range ofthe molecular sieve and is, in fact, a target operating pressure asopposed to a timed duration of pressure as utilized in a conventionalPSA system. Control of the process according to the present invention ismanaged by timing only, pressure only, or a combination of the two. Theadvantage of a pressure based system is that it may self adjust forcomponent wear such as valve response time. There is no calibratedorifice in the system upon which all other processes are criticallytimed. There is no gas flow through the sieve bed during the gasseparation process, which allows for a logical stopping point in theprocess such as a pause during the process while product gas is used.This provides for use in an OCD. For example, once a system according tothe present invention has achieved a desired product gas concentration,the concentration may be maintained through a shut down and restart, forexample so as to conserve battery life. The sieve bed can function as areservoir, which saves space. The process in the present invention isthus one of “counter-fill” as opposed to aprocess of “counter-flow”.Counter-fill is more efficient for product gas regeneration than“counter-flow” because the system does not vent product gas such asoxygen.

It is another object of the present invention to provide an OCD that hasthe ability to dynamically adjust the conserving ratio, that is, toprovide a dynamic conserving ratio as required by the patient (orprescribed by a doctor. Thus, the oxygen conserving device may use a 6:1ratio at the low flow equivalency setting but as the flow equivalencysetting is increased it may change it's conserving ratio to a lower orhigher conserving ratio as required by the patient. The adjustment ofthe settings relative to the minimum and maximum oxygen flow may bemodified depending on the requirements of the patient. Alternatively,the doctor may choose to prescribe a predetermined quantity of oxygenadministered per flow setting, as a direct volume of gas per bolus.

It is yet a further object of the present invention to provide a dynamicsensing of inspiration for the patient. Instead of triggering therelease of oxygen from a fixed negative pressure point, the conservingdevice would increase its sensitivity until inspiration was detected.Once inspiration was detected it would maintain the sensitivity levelunless further adjustment was required. If no inspiration was detectedit would automatically increase sensitivity until detected.Over-sensitivity may be detected by detecting the occurrence of unlikelyrespiratory rates in which case the system would decrease sensitivity.

The steps in a cycle of the oxygen concentration process according tothe present invention may be summarized in one aspect as follows:

-   -   (a) Atmospheric air is compressed into a first chamber from the        corresponding first feed end through a first conduit. The first        chamber is divided into two regions, one at each end with a        boundary therebetween (the boundary) created by a diffusion        plate mounted across the boundary which retains zeolite in a        feed end while the other end, the product end, is empty,        hereinafter referred to as the product end void space.    -   (b) Oxygen enriched gas is then vented from the empty product        end void space of the first chamber (the first product end void        space) through a second conduit and gas outfeed-line, for end        use, for example, by a patient.    -   (c) Oxygen enriched gas is then released from the first chamber,        through a third gas conduit having a third gas conduit intake at        the first boundary, that is the boundary between the first feed        end and the first product end void space.    -   (d) The oxygen enriched gas flows through the third gas conduit        and enters a second chamber, at the boundary between the second        product end (the second product end void space) and the second        feed end (the zeolite filled region), hereinafter also referred        to as the second boundary, of the second chamber.    -   (e) The oxygen enriched gas flow is directed from the second        boundary toward the feed end of the second chamber. This process        is hereinafter referred to as counter-fill.    -   (f) The first chamber is then vented to the atmosphere through a        first exhaust port on the first feed end, either to ambient        atmosphere or, for example, through a vacuum pump providing a        reduced pressure at the exhaust port.    -   (g) Atmospheric air is then compressed into the second chamber        from the second feed end.    -   (h) A portion of oxygen-enriched gas is then vented from the        second product end void space of the second chamber through the        second conduit and gas outfeed-line for end use.    -   (i) Oxygen enriched gas is then released at the boundary from        the second chamber, through the third gas conduit intake and        third gas conduit.    -   (j) The oxygen-enriched gas flows through the third gas conduit        and enters the first chamber at the first boundary.    -   (k) The oxygen enriched gas flow is directed from the first        boundary toward the first feed end of the first chamber.    -   (l) The second chamber is then vented to the atmosphere through        a second exhaust port on the second feed end, either to ambient        atmosphere or, for example, through a vacuum pump providing a        reduced pressure at the exhaust port.

The cycle is then repeated.

The present invention may also be characterized in a further aspect as agas concentrator for enriching a product component gas concentration ina gas, wherein the concentrator may include:

-   -   An air compressor.    -   An airtight first chamber separated into two adjacent sections        namely a hollow first product end and an adjacent first feed end        containing molecular sieve material for adsorbing a waste        component gas. The first feed end is separated from said first        product end by a first gas-permeable boundary member such as a        diffusion plate which may in one embodiment be a perforated        plate to accommodate gas transfer during counter-fill as defined        below. A second air-tight chamber includes a hollow second        product end and an adjacent second feed end containing molecular        sieve material for adsorbing the waste component gas, the second        feed end separated from said second product end by a second        gas-permeable boundary member such as a diffusion plate which        may in one embodiment be a perforated plate to accommodate gas        transfer during counter-fill and the opposing side of which is        perforated to allow for the transfer of gas between sieve filled        side of the sieve bed and the opposing hole which is open to the        empty side of the sieve bed.    -   The first feed end is in fluid communication with the compressor        through a first gas infeed line. The second feed end is in fluid        communication with the compressor through a second gas infeed        line. A first conduit common to both the first and second gas        infeed line, feeds or splits into the first and second gas        infeed lines from the compressor. A second gas conduit connects        said first and second product ends of the corresponding first        and second chambers in fluid communication with each other. The        second conduit cooperates with an outfeed line for delivery of        the product gas along said outfeed line to an end use. A third        gas conduit cooperates in fluid communication with said first        and second Boundaries corresponding to the first and second        chambers.    -   First and second exhaust ports are provided on, respectively,        the first and second feed ends of, respectively, the first and        second chambers for venting to atmosphere, or a vacuum source.    -   First, second, and third valve means and exhaust valve means,        and corresponding actuators, are mounted, respectively, on the        first, second, and third conduits, including their respective        infeed or outfeed lines, and on the first and second exhaust        ports for selective control of gas flow into and out of the        product ends and feed ends of the first and second chambers.    -   The first valve means provides for selective inflow of air from        the compressor to either of the first or second feed ends. The        exhaust valve means provides for selective exhausting, that is,        outflow of gas from either the first or second feed ends        passively or with a vacuum source. The second valve means        provides for selective gas flow from the first or second product        ends, and their respective first or second product end void        spaces, to the gas outfeed line for end use of the gas. The        third valve means, which may include one or more valves,        provides for selective counter-fill between the first and second        boundaries. When actuated in sequence oxygen enriched gas is        generated alternatingly in the first and second chambers and fed        sequentially for end use through the gas outfeed line, the first        and second product ends alternatingly automatically recharging        and exhausting during the outfeed and counter-fill.

A gas flow controller may be provided for controlling actuation ofvarious valves and/or valve means, so that said valves and/or valvemeans cooperate to regulate gas flow through said conduits and lines soas to sequentially, in repeating cycles:

-   -   (a) prevent the gas from flowing between the first and second        chamber and allow compressed air from the compressor into the        first chamber during a first gas pressurization phase, whereby        the first container is pressurized to a threshold pressure level        to create a first enriched gas packet in the first product end        having an incrementally enriched product component gas (such as        oxygen) concentration, and opening the second chamber exhaust        valve means so as to expel, for example to atmosphere or to a        vacuum source, the gaseous contents of the second chamber,    -   (b) prevent the gas from flowing between either of the first or        second chambers and the compressor and allow a regulated amount        of the first enriched gas packet to flow from the first product        end into the second gas conduit for delivery of the product        component gas for the end use, downstream along the second gas        conduit and the gas outfeed line,    -   (c) prevent the gas from flowing between either of the first or        second chambers and the compressor or between either of the        chambers and the gas outfeed-line, and allow the first enriched        gas packet to flow between the boundaries of the first and        second chambers from the third gas conduit during a first        enriched gas packet counter-fill phase, whereby the first        enriched gas packet flows from the pressurized first chamber to        the lower pressure second chamber,    -   (d) prevent the gas from flowing between the chambers and        actuate the compressor to pressurize the second chamber to the        threshold pressure level to create a second enriched gas packet        and, open the first chamber exhaust valve means so as to expel,        for example to atmosphere or to a vacuum source, the gaseous        contents of the first chamber,    -   (e) prevent the gas from flowing between either of the chambers        and the compressor and allow a regulated amount of the second        enriched gas packet to flow from the second product end into the        second gas conduit for delivery of the product component gas for        the end use, downstream along the second gas conduit and the gas        outfeed line,    -   (f) prevent the gas from flowing between either of the chambers        and the compressor or between either of the chambers and the gas        outfeed valve, and allow the second enriched gas packet to flow        between the boundaries of the first and second chambers through        the third gas conduit, during a second enriched gas packet        counter-fill phase, whereby the second enriched gas packet flows        from the pressurized second chamber to the lower pressure first        chamber.

In a further aspect, the present invention may be characterized as a gasconcentrator apparatus for enriching a product gas concentration in agas, wherein the apparatus includes: a pressure differential means suchas a compressor, an air-tight first chamber having a hollow firstproduct end and an adjacent first feed end containing molecular sievematerial for adsorbing a waste component gas, wherein the first feed endis separated from the first product end by a gas-permeable firstboundary member, a second air-tight chamber having a hollow secondproduct end and an adjacent second feed end containing molecular sievematerial for adsorbing the waste component gas, wherein the second feedend is separated from the second product end by a gas-permeable secondboundary member, wherein the first feed end is in fluid communicationwith the pressure differential means through a first gas infeed conduit,and wherein the second feed end is in fluid communication with thepressure differential means through a second gas infeed conduit, andwherein a second gas conduit connects in fluid communication with, andselectively between, the first and second product ends, and wherein athird gas conduit cooperates in fluid communication between and to thefirst and second gas permeable boundary members, and wherein the secondgas conduit cooperates in fluid communication with an outfeed line fordelivery of the product gas along the outfeed line to an end use, thefirst and second feed ends having, respectively, first and secondexhaust ports for selectively venting the first and second feed ends,first valve means for selective inflow of air from the compressor toeither of the first or second feed ends, exhaust valve means forselective exhausting of gas from either the first or second feed ends,second valve means for selective gas flow from the first or secondproduct ends to the gas outfeed line for end use of the gas, and thirdvalve means for selective gas flow between and to the first and secondboundary members so that, when the valve means are actuated in sequence,product gas enriched gas is generated alternatingly in the first andsecond chambers and fed sequentially for end use through the gas outfeedline.

A gas flow controller controls actuation of the valve means to regulategas flow through the conduits and the outfeed line so as tosequentially, in repeating cycles:

-   -   (a) prevent the gas from flowing between the first and second        chamber and allow compressed air from the compressor into the        first chamber during a first gas pressurization phase, wherein        the first container is pressurized to a threshold pressure level        to create a first enriched gas packet in the first product end        having an incrementally enriched product gas concentration, and        opening the second chamber exhaust valve means so as to expel        the gaseous contents of the second chamber,    -   (b) prevent the gas from flowing between either of the first or        second chambers and the compressor and allow a regulated amount        of the first enriched gas packet to flow from the first product        end into the second gas conduit for delivery of the product gas        for the end use downstream along the second gas conduit and the        outfeed line,    -   (c) prevent the gas from flowing between either of the first or        second chambers and the compressor or between either of the        chambers and the outfeed-line, and allow the first enriched gas        packet to flow from the first boundary member to the second        boundary member in the third gas conduit wherein the first        enriched gas packet flows from a pressurized the first chamber        to a lower pressure the second chamber,    -   (d) prevent the gas from flowing between the chambers and        actuate the compressor to pressurize the second chamber to the        threshold pressure level to create a second enriched gas packet        and open the first exhaust valve means so as to expel to        atmosphere the gaseous contents of the first chamber,    -   (e) prevent the gas from flowing between either of the chambers        and the compressor and allow a regulated amount of the second        enriched gas packet to flow from the second product end into the        second gas conduit for delivery of the product component gas for        the end use downstream along the second gas conduit and the        outfeed line,    -   (f) prevent the gas from flowing between either of the chambers        and the compressor or between either of the chambers and the        outfeed valve, and allow the second enriched gas packet to flow        between the first and second boundary members through the third        gas conduit wherein the second enriched gas packet flows from a        pressurized the second chamber to a lower pressure the first        chamber.

The boundary members may be gas diffusers. The third conduit hasopposite first and second ends, the first and second open ends havingcorresponding first and second apertures therein, and wherein the firstand second apertures are adjacent and spaced from, respectively, thefirst and second boundary members. The first and second apertures may besubstantially parallel to, respectively, the first and second boundarymembers. The second conduit may be a tube.

First and second infeed gas diffusers may be mounted adjacent,respectively, the first and second gas infeed conduits so as to diffusegas fed into the first and second feed ends through the first and secondgas infeed conduits, whereby the molecular sieve material is sandwiched,respectively, between first boundary member and the first infeed gasdiffuser, and between the second boundary member and the second infeedgas diffuser.

First and second gas plenums may be provided, respectively, between thefirst gas infeed conduit and the first infeed gas diffuser, and betweenthe second gas infeed conduit and the second infeed gas diffuser. Firstand second gas manifolds may be mounted respectively, adjacent andbetween the first end of the second conduit and the first boundarymember, and adjacent and between the second end of the second conduitand the second boundary member.

The method of the present invention may further include:

-   -   a) providing a means for detecting a drawing of the oxygen        enriched gas to the end use from the second conduit, a means for        detecting a pressure drop below a lower threshold pressure in a        reservoir of the oxygen enriched gas cooperating in fluid        communication with the second conduit wherein the pressure drop        is due to the drawing of the oxygen enriched gas from the second        conduit, a means for signalling the pressure drop to the means        for controlling gas flow;    -   b) establishing a pressurized reservoir of the oxygen enriched        gas for delivery through the second conduit for the end use;    -   c) ceasing the flow of gas into or between the first and second        chambers once the pressurized reservoir of the oxygen enriched        gas is established until the pressure drop below the lower        threshold pressure, upon the detection of which re-commencing        the flow of gas into or between the first and second chambers.

The method may further include providing a discrete reservoir for thereservoir of the oxygen-enriched gas.

The product ends may in one embodiment provide the reservoir of theoxygen-enriched gas.

The method may further include the step of monitoring pressure in thereservoir of the oxygen-enriched gas. The method may further include thestep of ceasing production of the oxygen-enriched gas upon detection ofpressure equal to or greater than an upper threshold pressure in thereservoir of the oxygen enriched gas. The method may further includeproviding a means for selectively varying a delivery volume of theoxygen-enriched gas delivered per the drawing to the end use. The methodmay further include providing a means for selectively varying thesensitivity of the means for detecting a drawing of the oxygen-enrichedgas.

The method may further include the steps of:

-   -   a) pre-setting a selectively adjustable oxygen conservation        ratio in the means for controlling gas flow and a selectively        adjustable drawing sensitivity,    -   b) monitoring for pressure change, which according to the        drawing sensitivity, is indicative of drawing of the oxygen        enriched gas from the second conduit for the end use,    -   c) upon detection of the sharp pressure change, allowing the        oxygen enriched gas to flow from the reservoir along the second        conduit to the end use in a volume according to the pre-set        oxygen conservation ratio.

The method may further include the steps of:

-   -   a) monitoring time intervals between or frequency of sequential        the drawings of the oxygen enriched gas,    -   b) selectively varying the conservation ratio and/or the drawing        sensitivity so as to:        -   (i) increase the sensitivity upon an increase in the time            interval or drop in        -   (ii) the frequency relative to first threshold values;        -   (iii) decrease the sensitivity upon a decrease in the time            interval or increase in the frequency relative to second            threshold values;        -   (iv) increase the conservation ratio so as to decrease            supply of the oxygen enriched gas if the conservation ratio            is low and the drawing frequency is low; or,        -   (v) decrease the conservation ratio so as to increase supply            of the oxygen enriched gas if the conservation ratio is high            and the drawing frequency is high.

In a broader sense, the present invention operates on a gaseous mixtureof a less strongly adsorbed (or light) component and a more stronglyadsorbed (or heavy) component, which is more strongly adsorbed by anadsorbent, where the light component is selectively separated from thegaseous mixture in a PSA process, as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is, in perspective view, an oxygen concentrating apparatusaccording to one embodiment of the present invention.

FIG. 2 is a sectional view along line 2-2 in FIG. 1 wherein a firstzeolite container is being pressurized with compressed air, and whereina second zeolite container is being vented to atmosphere.

FIG. 3 is the sectional view of FIG. 2 wherein no further compressed airis being pumped into the first zeolite container and a first portion ofthe enriched oxygen gas in the product end of the first zeolitecontainer is being bled off to the patient through a gas outfeed line.

FIG. 4 is the sectional view of FIG. 3, wherein the flow of enrichedoxygen to the patient from the first zeolite container has been stopped,and a further portion of the enriched oxygen gas from the boundary ofthe first zeolite container is being fed into the zeolite region, thefeed end, of the second zeolite container.

FIG. 5 is the sectional view of FIG. 4 wherein the first zeolitecontainer is vented to atmosphere and the second zeolite container isbeing pressurized with compressed air.

FIG. 6 is the sectional view of FIG. 5 wherein pressurization of thesecond container has stopped, and a first portion of the enriched oxygengas from the product end of the second zeolite container is bled off tothe patient, and wherein the first zeolite container is being vented toatmosphere.

FIG. 7 is the sectional view of FIG. 6 wherein the flow of oxygenenriched gas to the patient has been stopped, and a further portion ofthe oxygen enriched gas from the boundary of the second zeolitecontainer is being fed into the zeolite region, the feed end, of thefirst zeolite container.

FIG. 8 is the sectional view of FIG. 7 wherein the counter-fillpressurization of the first zeolite container has stopped, and the firstzeolite container is once again being pressurized with compressed air,and the second zeolite container is once again being vented toatmosphere.

FIG. 9 is an enlarged view of a portion of FIG. 5.

FIG. 10 is a diagrammatic view of a demand cycle PSA system according toan alternative embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The mechanics of a one half-cycle will now be described.

In the present invention, wherein like reference numerals denotecorresponding parts in each view, a first container is pressurized withair by a compressor (shown in FIG. 3). Advantageously, the firstcontainer contains a high mole fraction of oxygen and is pressurizedwith atmospheric air. Nitrogen will adsorb to the zeolite more readilythan oxygen. As a result there will be a higher concentration of oxygenin the zeolite void space and the product end void space than there wasin the original air mixture. Ensuring the starting oxygen mole fractionis high can produce high oxygen concentration end use gas. This ensureseffectively all the nitrogen from atmospheric pressurization can beadsorbed by the zeolite.

Some of the product end void space gas is then released for end use fromthe first container.

When a gas mixture is vented from any pressurized zeolite container, theoxygen enriched zeolite void space gas will be vented first. As aresult, most of the oxygen will be evacuated before the nitrogen.However, after the oxygen-enriched gas is vented from the zeolite in thecontainer, nitrogen is immediately released from the zeolite and thusmay dilute the oxygen concentration.

In the present invention, first container 10 has a first product end 10a having a cavity or product end void space 14 that does not containnitrogen-releasing zeolite. The zeolite 16 is confined to first feed end10 b. As a result, when first container 10 is vented to deliveroxygen-enriched gas, the first released gas has little or no addednitrogen content. Thus it is desirable that all the end use productcomponent gas, that is, oxygen-enriched gas, should be vented from theproduct end void space 14.

It is important to consider the relative volumes of feed end 10 b toproduct end 10 a. If the product end 10 a is too small, then the end usegas volume will not be the maximum volume attainable. If the product end10 a, that is, the product end void space 14 is too large, then thezeolite will not be able to adsorb all the nitrogen during atmosphericpressurization and dilution of the product end void space gas (that isdilution of oxygen with nitrogen) will result. Testing of one embodimentof the present invention has shown the following ratio to be an optimumfor the separation of oxygen and nitrogen with a zeolite having abulk-loading factor of 3:1. That is, using a zeolite filled containerthat can hold three times the volume of gas at the operational pressurescompared to an empty container of the same volume as the volume of thezeolite container, and assuming 100% of the nitrogen is adsorbed by thezeolite, then 79 parts nitrogen in air will fill a volume of 26.3 parts.Add this to the 21 parts of oxygen in the air and the zeolite filledportion of the container becomes 55.6%. The product end void space 14should therefore be 44.4% of the zeolite container. A perforated barriersuch as the mid diffuser plate better described below may be mountedtherebetween to partition or demark the boundary. This principle alsoapplies to the separation of other target gasses as well.

End-use concentrated oxygen is bled off via second conduit 18 and gasoutfeed line 18 a and then the second zeolite container 20 iscounter-filled. During the counter-fill stage, the first container 10 ispartially depressurized through third conduit 22 to feed oxygen enrichedgas to pre pressurize or counter-fill second container 20. Thissufficiently increases the mole fraction of oxygen in second container20 to produce high oxygen fraction zeolite void space gas in the zeolitevoid space 24 of zeolite 26. The oxygen-enriched gas fed into the secondfeed end 20 a of second container 20 during the counter-fill takes up aportion of the volume in the second container 20 that would have beentaken up by air. As a result, the nitrogen content of the air, fromatmospheric pressurization that is from using compressor 8 cannot becomelarge enough to dilute the output gas concentration. This counter-fillgas volume, once produced, is in part cyclically re-used over and overagain.

Oxygen desorbs faster than nitrogen. Thus, at the end of counter-fill,the nitrogen content of the counter-fill gas coming into container 20from container 10 is very high. If the counter-fill gas volume fed intocontainer 20 from container 10 is too large, then the net oxygenconcentration of the zeolite void space gas in container 20 will dropbelow that of air. In that event, the gas volume that can be deliveredfor end use will be reduced.

A gas separating system will not work efficiently if the endcounter-fill gas, that is, the high nitrogen concentration gas at theend of the counter-fill from one container into the other, ends up inthe product end void space of either container.

To ensure that this end counter-fill gas does not end up in the productend void space of either container, the third gas conduit 22 extendsthrough the product end void space of both containers to themid-diffuser plates of boundary 28 and the boundary 30 of containers 10and 20 respectively. Boundaries 28 and 30 and their correspondingmid-diffuser plates provide a physical means to manage the volumetricratio of the feed end to the product end. Mid-diffuser plates may befelt-covered rigid perforated gas diffuser plates as described below.

The counter-fill gas flows from container 10 to container 20 is asfollows:

Due to the pressure differential between container 10 and container 20,when the third valve 32 is opened, aperture 22 a to third gas conduit 22in container 10 becomes a point vacuum source. Counter-fill gas is drawnto the point vacuum source of aperture 22 a from both the zeolite voidspace 13 and from the product end void space 14. Because the gasreleased from the zeolite 16 is drawn to the point vacuum source, verylittle nitrogen-enriched gas reaches the product end void space.

The counter-fill gas flows through third conduit 22 and out of aperture22 b at boundary 30 in container 20. The counter-fill gas is directedtoward the zeolite 26 in feed end 20 b in container 20.

Counter-fill is ceased while container 10 is still at a pressure, whichis above atmospheric. The high nitrogen content waste gas may thus bevented to atmosphere from the feed end 10 b of container 10 without theuse of mechanical energy or with a vacuum assist. If this waste gas werevented from the product end, then the product end void space 14 would becontaminated with high nitrogen content gas.

As noted above, atmospheric air during pressurization using compressor 8is introduced into container 10 from the feed end 10 b. The vent conduitor exhaust port 34 on the feed end 10 b of container 10 isadvantageously a separate conduit from the atmospheric infeed line 36from the compressor 8. After the completion of the vent cycle, the ventconduit is full of nitrogen-enriched gas. If this conduit were connectedto the atmospheric pressurization infeed lines 36 or 38, then thenitrogen would be blown back into container 10 during the next cycle.

Operation of the opening and closing of the valves, as set out below,may advantageously be automated, for example controlled by a gas flowcontroller 40 such as seen in FIG. 3. The valves are illustrated asbeing manually actuated for ease of understanding and for clarity of theillustrations, and are not intended to be so limited. The reference tovalve means herein is intended to encompass and include both valves andactuators.

The zeolite 16 and 26, in containers 10 and 20 respectively, aresandwiched by four porous retaining plates; namely, plates 42 a and 42 bin container 10 and plates 44 a and 44 b in container 20 and, thussandwiched. The porous plates may be covered with felt 45 or othermembranes or porous material to assist in diffusing the flow of gas andto help contain the zeolite particles, which, although illustrated asbeing relatively large, are usually much smaller, for example particlesof 0.5 mm in diameter. The plates and felt are mounted to enclose thezeolite filled regions.

With reference now to the operation of the device according to thepresent invention, in the start-up condition, first and second zeolitecontainers 10 and 20 respectively, are at atmospheric pressure. Firstzeolite container 10 is pressurized with atmospheric air from compressor8. Air from compressor 8, passes through first conduit 46, junction 46a, conduit 36 and valve 48, at the feed end 10 b of zeolite container10.

Oxygen enriched gas is then vented from product end void space 14 at theproduct end 10 a of first zeolite container 10, to be delivered to thepatient or other end use, through valve 50, second conduit 18, and gasoutfeed line 18 a.

Oxygen enriched gas is then vented from container 10 by way of thirdconduit 22 through valve 32 so as to partially pressurize container 20.Container 10 is then vented to the atmosphere from the feed end 10 b,through valve 52 and exhaust port 34, and container 20 pressurized withatmospheric air from compressor 8, through first conduit 46, junction 46a, second gas infeed line 38, valve 54, at the feed end 20 b ofcontainer 20.

Oxygen enriched gas is then vented from product end void space 56 atproduct end 20 a, of container 20, to be delivered to the patient orother end use, through valve 58, second conduit 18, and gas outfeed line18 a.

Oxygen enriched gas is then vented from container 20 to container 10 byway of third conduit 22 through valve 32 so as to partially pressurizecontainer 10.

Container 20 is vented to the atmosphere from the feed end 20 b, throughsecond exhaust port 60 and valve 62.

The cycle is repeated as air is pressurized into first zeolite container10.

What follows is a more detailed description of the device duringstart-up and during one cycle of operation:

In the start-up condition containers 10 and 20 are at atmosphericpressure. All valves may be closed.

As seen in FIG. 2, valves 32, 50 and 52 are closed. First zeolitecontainer 10 is then pressurized by compressor 8 so as to causepressurized atmospheric air to flow through conduits 46 and 36 andthrough open valve 48 into feed end 10 b.

As seen in FIG. 3, valve 48 is closed, the compressor 8 may be shut off,and valve 50 opened so as to vent oxygen enriched gas from product endvoid space 14 in product end 10 a to an end user such as a patient viaconduits 18 and 18 a.

As seen in FIG. 4, valves 50 and 62 are closed and valve 32 opened.Oxygen enriched gas is then vented from container 10 by way of conduit22 through valve 32 so as to partially pressurize container 20. Theenriched gas leaves conduit end 22 b of conduit 22 into an interfacebetween the product end void space and the zeolite end, which, asillustrated, may be a partially enclosed manifold at boundary 30 boundedby a cup or rimmed plate 31 through which conduit end 22 b is mountedand rigid perforated mid-diffuser plate 44 a, advantageously covered byporous gas diffusing membrane or material such as felt 45.

As seen in FIGS. 5 and 9, valve 32 is closed and valve 54 opened so thatcompressed atmospheric air from compressor 8 flows via conduit 46,junction 46 a, conduit 38, and through valve 54 into feed end 20 b ofcontainer 20 where the gas is distributed in gap or manifold 55 fordiffusion through the perforations in diffuser plate 44 b and felt 45.The object is to provide a means for evenly distributing the gas flowacross the sieve bed. Container 10 has the same diffuser arrangement ascontainer 20. Valve 52 is opened so as to vent feed end 10 b to theatmosphere.

As seen in FIG. 6, valve 54 is closed, and compressor 8 may be shut off.Valve 58 is opened so as to vent oxygen-enriched gas from product endvoid space 56 in product end 20 a through valve 58 and, conduits 18 and18 a to an end user such as a patient.

As seen in FIG. 7, valve 58 is closed and oxygen enriched gas ventedfrom container 20 to container 10 by way of conduit 22 through valve 32so as to partially pressurize container 10.

As seen in FIG. 8, valve 32 is closed and valve 62 is opened, so as tovent container 20 and valve 48 opened to commence the cycle again withpressurization of container 10.

A product gas concentrator, such as the oxygen concentrator describedabove may operate as the product gas source in an OCD such as depictedin FIG. 10. An OCD may complement the operation of a PSA system such asthat according to the present invention in allowing for shutdown andre-start of the PSA system to thereby conserve the PSA system battery orbatteries when the reservoir is sufficiently pressurized withconcentrated gas. Thus as seen in FIG. 10, pressure swing adsorptionsystem 1 such as the oxygen concentrator according to the presentinvention as described above generates oxygen enriched gas. The oxygenenriched gas flows through gas conduit 102, first valve 103, conduit104, to gas reservoir 105. Alternatively the function of gas reservoir105 is served by the product end void spaces in the embodiment of thepresent invention described above. Thus the oxygen-enriched gas isstored in either the gas reservoir 105 or the product end void spaces 14and 56. The gas pressure in reservoir 105 is sensed by a first sensor107 in fluid communication with the gas reservoir 105 by way of gasconduit 106. The first sensor 107 sends gas reservoir 105 pressure datato a logic controller 116 via a network such as communication means 200.When the gas reservoir 105 reaches a pre-determined maximum operatingpressure, the logic controller 116 stops the pressure swing adsorptionsystem 1 from generating oxygen, thus conserving energy. The logiccontroller 116 closes the first valve 103 to stop the oxygen-enrichedgas stored in the gas reservoir 105 from flowing back to the pressureswing adsorption system 1.

The patient receives the oxygen-enriched gas by way of a cannula (notshown) connected to an outlet 113 of gas conduit 112. Sudden changes inpressure caused by inspiration are detected in the gas conduit 113 byway of a second sensor 115 connected to gas conduit 110 at junction 112.The second sensor 115, communicates the sudden change in pressure to thelogic controller 116. The logic controller 116 opens a second valve 109to release the oxygen-enriched gas from the gas reservoir 105, by way ofgas conduit 110, to the patient through outlet 113. After apre-determined period of time, the logic controller 116 closes thesecond valve 109 stopping the release of oxygen-enriched gas from thegas reservoir 105. When the first sensor 107 detects a minimumpre-determined pressure in the gas reservoir 105 the logic controller116 turns on the pressure swing adsorption system 1, repeating thecycle. Thus again, pressure measurements are detected from the patientsupply 113. Changes in pressure propagate through gas conduit 110,junction 12 and gas conduit 140.

Pressure measuring means 115 in fluid communication with gas conduit 140continuously transmits pressure measurements via measurementtransmitting means to logic controller 116.

The logic controller 116 stores in memory times and pressure values.Thus, logic controller 116 stores a memory value for oxygen deliverytime for both a high and a low conserving ratio. Logic controller 116also stores in memory a value for high breath (that is, inspiration ordrawing) sensitivity. Logic controller 116 also stores in memory thesettings for the values in use. For example, logic controller 116 may beset so that valve 109 actuation is based on a high breath (that isinspiration) sensitivity and a high conserving ratio gas deliveryvolume.

If logic controller 116 identifies a sharp change in pressure in the gasconduit, within a preset pressure threshold range, controller 116transmits logic output signals by way of logic communication means 200to actuable valve 109 to open the value for a predetermined time. If thelogic controller 116 identifies a sharp change in pressure, but thefrequency, that is the number within a certain time, of the detectedpressure change is too high, then the controller lowers the breathsensitivity setting. If logic controller 116 identifies a sharp changein pressure immediately after oxygen delivery has been delivered, thelogic controller 116 ignores the signal to act as a stabilizer ordebounce feature. If logic controller 116 identifies a prolonged periodof time in which no sharp changes in pressure have occurred, the logiccontroller changes the setting so as to increase the breath detectionsensitivity. If logic controller 116 identifies a sharp change inpressure, and the frequency of the change is too high, and the breathdetection sensitivity is low, then the controller changes the oxygendelivery time to a low or lower conserving ratio to increase the oxygenvolume delivered to the patient per breath. If logic controller 116 isset to a low conserving ratio and the rate of sharp changes in pressurein the gas conduit is reduced then logic controller 116 changes thesettings so as to increase the oxygen conserving ratio in order toreduce oxygen consumption.

PSA Analysis

The adsorbent-filled portion of the present vessel functions similarlyto any other PSA adsorber. The empty space is different, however. Aspointed out above, some previous adsorbers employed empty space toretain gas in order to purge the adsorbent bed, and thereby to completeits regeneration. Hence, it is a convenience only for storage. In thepresent case, the volume serves an additional purpose that is explainedbelow.

Most PSA systems are intentionally designed to have very little excessvolume at the product-end of the adsorber. Consequently gas that reachesthat end, by passing through the adsorbent, is extracted and stored in aseparate receiver vessel. Subsequently, a portion of that gas isadmitted back into the adsorbent bed at the same end, first at lowpressure for purging it, which means that decompression of the gasoccurred, or under increasing pressure, that is, during which theadsorbent is repressurized. There is a decrease in pressure of the gasgoing into the receiver, or flow would not occur. Similarly, there is adecrease in pressure between the receiver and the adsorber, when part ofthe product gas is recycled, or the gas would not flow. The pressuredrop is associated with throttling (since no useful work is done), butthe drop in pressure equates to a loss of the ability to do work.

Work

The gas in the space will be treated as an ideal gas, for simplicity.The same concepts apply whether that assumption is valid or not. If thegas is non-ideal, the calculations are merely more complicated, but thesame thermodynamic principles apply, e.g., conservation of energy and ofmaterial.

It is desired to understand what happens to the gas in the product-endreservoir as pressure is increased by admitting feed.

-   -   1. As feed is admitted, the heavy component is retained by the        adsorbent, and the light component percolates through the        adsorbent.    -   2. As the light gas percolates, the light gas flows into the        product-end reservoir causing its pressure to increase.    -   3. A material balance occurs on the gas contained in the        product-end reservoir, employing the ideal gas law.    -   4. An energy balance occurs on the gas contained in the        product-end reservoir, again employing the ideal gas law.

Normally, a product pressurized PSA process is more efficient than afeed pressurized PSA process, assuming adiabatic conditions. Such is notthe case for the PSA process according to the present invention and suchphenomenon, although applicants do not wish to be held to any one theoryof operation, may be due to the ability of the present PSA processdesign to recover the temperature component, which would otherwise belost.

Additional concepts for modifying the PSA system according to thepresent invention disclosed herein include the following.

Air Flow Ramping

In the interest of maintaining plug flow within the sieve bed, it may bebeneficial to balance flow into the bed with pressure in the bed. Forexample, if we have a large diameter sieve bed and want to minimize N₂incursion into the PVS (Product Void Space) we could start thepressurization stage with a lower flow rate and increase it as pressurebuilds in the sieve bed.

Series Sieve Beds

It may be desirable to extract more than one product gas in a singlepass. Arranging a series of sieve beds like beads on a string wouldallow for each sieve bed to be optimized for its target gas. Overallvolume of the sieve bed could be tailored as well as the type of sieve,sieve volume and product void space.

Staged Pressurization

In the above configuration, it would be possible to place a pump at eachsieve bed inlet. This may decrease the pressure drop across the sievebed and be more electrically efficient.

It would also allow for independent working pressures at each stage ofseparation.

Variable Product Void Space

In one variation the PVS is made adjustable using a screw to allow forprecise tuning of the sieve bed ratio. In another variation a sensormonitors a fluctuating inlet gas concentration and adjusts a piston (orother positive displacement device), which adjusts the PVS such that atthe end of a pressurization stage the sieve bed has dynamically adjusteditself to the ideal PVS to Sieve Space ratio.

Instrumentation, controls, feeders, tanks, fittings, valves, and otherauxiliary appurtenant equipment are to be provided where necessary,desirable, or convenient in conventional fashion. Materials ofconstruction are conventional for the materials being handled and thepressures/temperatures expected in the process and where corrosion orerosion is expected. Insulation is to be provided where necessary formaintaining temperature and conserving energy. Various of the tanks andlines illustrated can be in multiple, series, cascade, or parallelconnected for additional treating time or capacity.

While the invention has been described with reference to variousembodiments, those skilled in the art will understand that variouschanges may be made and equivalents may be substituted for elementsthereof without departing from the scope and essence of the invention.In addition, many modifications may be made to adapt a particularsituation or material to the teachings of the invention withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the invention not be limited to the particular embodimentsdisclosed, but that the invention will include all embodiments fallingwithin the scope of the appended claims. In this application all unitsare in the metric system and all amounts and percentages are by weight,unless otherwise expressly indicated.

1. A gas concentrator apparatus for enriching a product gasconcentration in a gas, the apparatus comprising: a pressuredifferential member, an air-tight first chamber having a hollow firstproduct end and an adjacent first feed end containing molecular sievematerial for adsorbing a waste component gas, wherein said first feedend is separated from said first product end by a gas-permeable firstboundary member, a second air-tight chamber having a hollow secondproduct end and an adjacent second feed end containing molecular sievematerial for adsorbing the waste component gas, wherein said second feedend is separated from said second product end by a gas-permeable secondboundary member, wherein said first feed end is in fluid communicationwith said pressure differential member through a first gas infeedconduit, and wherein said second feed end is in fluid communication withsaid pressure differential member through a second gas infeed conduit,and wherein a second gas conduit connects in fluid communication with,and selectively between, said first and second product ends, and whereina third gas conduit cooperates in fluid communication between and tosaid first and second gas permeable boundary members, and wherein saidsecond gas conduit cooperates in fluid communication with an outfeedline for delivery of the product gas along said outfeed line to an enduse, said first and second feed ends having, respectively, first andsecond exhaust ports for selectively venting said first and second feedends, a first valve for selective inflow of air from said compressor toeither of said first or second feed ends, an exhaust valve for selectiveexhausting of gas from either said first or second feed ends, secondvalve for selective gas flow from said first or second product ends tosaid gas outfeed line for end use of the gas, and a third valve forselective gas flow between and to said first and second boundary membersso that, when said valves are actuated in sequence, product gas enrichedgas is generated alternatingly in said first and second chambers and fedsequentially for end use through said gas outfeed line, a gas flowcontroller for controlling actuation of said valves to regulate gas flowthrough said conduits and said outfeed line so as to sequentially, inrepeating cycles: (a) prevent the gas from flowing between the first andsecond chamber and allow compressed air from said compressor into saidfirst chamber during a first gas pressurization phase, wherein saidfirst container is pressurized to a threshold pressure level to create afirst enriched gas packet in said first product end having anincrementally enriched product gas concentration, and opening saidsecond chamber exhaust valve means so as to expel the gaseous contentsof said second chamber, (b) prevent the gas from flowing between eitherof said first or second chambers and said compressor and allow aregulated amount of said first enriched gas packet to flow from saidfirst product end into said second gas conduit for delivery of theproduct gas for the end use downstream along said second gas conduit andsaid outfeed line, (c) prevent the gas from flowing between either ofsaid first or second chambers and said compressor or between either ofsaid chambers and said outfeed-line, and allow the first enriched gaspacket to flow from said first boundary member to said second boundarymember in said third gas conduit wherein the first enriched gas packetflows from a pressurized said first chamber to a lower pressure saidsecond chamber, (d) prevent the gas from flowing between said chambersand actuate said compressor to pressurize said second chamber to thethreshold pressure level to create a second enriched gas packet and opensaid first exhaust valve means so as to expel to atmosphere the gaseouscontents of said first chamber, (e) prevent the gas from flowing betweeneither of said chambers and said compressor and allow a regulated amountof the second enriched gas packet to flow from said second product endinto said second gas conduit for delivery of the product component gasfor the end use downstream along said second gas conduit and saidoutfeed line, (f) prevent the gas from flowing between either of saidchambers and said compressor or between either of said chambers and saidoutfeed valve, and allow the second enriched gas packet to flow betweensaid first and second boundary members through said third gas conduitwherein the second enriched gas packet flows from a pressurized saidsecond chamber to a lower pressure said first chamber.
 2. The apparatusof claim 1 wherein said boundary members are gas diffusers.
 3. Theapparatus of claim 2 wherein said third conduit has opposite first andsecond ends, said first and second open ends having corresponding firstand second apertures therein, and wherein said first and secondapertures are adjacent and spaced from, respectively, said first andsecond boundary members.
 4. The apparatus of claim 3 wherein said firstand second apertures are substantially parallel to, respectively, saidfirst and second boundary members.
 5. The apparatus of claim 4 whereinsaid second conduit is a tube.
 6. The apparatus of claim 2 furthercomprising first and second infeed gas diffusers mounted adjacent,respectively, said first and second gas infeed conduits so as to diffusegas fed into said first and second feed ends through said first andsecond gas infeed conduits, whereby said molecular sieve material issandwiched, respectively, between first boundary member and said firstinfeed gas diffuser, and between said second boundary member and saidsecond infeed gas diffuser.
 7. The apparatus of claim 6 wherein saidthird conduit has opposite first and second ends, said first and secondopen ends having corresponding first and second apertures therein, andwherein said first and second apertures are adjacent and spaced from,respectively, said first and second boundary members.
 8. The apparatusof claim 7 further comprising first and second gas plenums,respectively, between said first gas infeed conduit and said firstinfeed gas diffuser, and between said second gas infeed conduit and saidsecond infeed gas diffuser.
 9. The apparatus of claim 8 furthercomprising first and second gas manifolds mounted respectively, adjacentand between said first end of said second conduit and said firstboundary member, and adjacent and between said second end of said secondconduit and said second boundary member.
 10. The apparatus of claim 9wherein said sieve material is zeolite, said product gas is oxygen, saidwaste component gas is nitrogen, and said pressure differential meansincludes a compressor.
 11. A method of increasing the oxygenconcentration of a gas, comprising: a) providing first and secondchambers in fluid communication with one, wherein said first chamber hasa first feed end containing first molecular sieve material for adsorbingnitrogen and a first product end separated from said first feed end by agas permeable first boundary member which restricts said first molecularsieve material to said first feed end, and wherein said second chamberhas a second feed end containing second molecular sieve material foradsorbing nitrogen and a second product end separated from said secondfeed end by a gas permeable second boundary member which restricts saidsecond molecular sieve material to said second feed end, wherein a firstconduit selectively supplies compressed air to said first or second feedends, wherein a second conduit selectively supplies gas from said firstor second product ends to an end use, and wherein a third conduitselectively supplies gas between and to said first and second boundarymembers; and providing a means for controlling as flow, and, byoperation of said means for controlling gas flow, said method, in onecycle of a plurality of cycles, comprising the steps of: b) compressingair-by-air compression means into said first chamber from said firstfeed end through said first conduit; c) delivering oxygen enriched gasfrom said first product end through said second conduit for said enduse; d) releasing oxygen-enriched gas from the first chamber to saidsecond chamber through said third gas conduit; e) venting said firstchamber as exhaust from said first feed end; f) compressing air intosaid second chamber from said second feed end; g) delivering oxygenenriched gas from said second product end through said second conduitfor end use; h) releasing oxygen enriched gas from said second chamberto said first chamber through said third gas conduit; and, i) ventingsaid second chamber as exhaust from said second feed end.
 12. The methodof claim 11 comprising the step of providing gas diffusers as said firstand second boundary members.
 13. The method of claim 12 wherein saidthird conduit has opposite first and second ends, said first and secondopen ends having corresponding first and second apertures therein, andwherein said first and second apertures are adjacent and spaced from,respectively, said first and second boundary members.
 14. The method ofclaim 13 wherein said first and second apertures are substantiallyparallel to, respectively, said first and second boundary members. 15.The method of claim 14 wherein said second conduit is a tube.
 16. Themethod of claim 12 further comprising first and second infeed gasdiffusers mounted adjacent, respectively, said first and second gasinfeed conduits so as to diffuse gas fed into said first and second feedends through said first and second gas infeed conduits, whereby saidmolecular sieve material is sandwiched, respectively, between firstboundary member and said first infeed gas diffuser, and between saidsecond boundary member and said second infeed gas diffuser.
 17. Themethod of claim 16 wherein said third conduit has opposite first andsecond ends, said first and second open ends having corresponding firstand second apertures therein, and wherein said first and secondapertures are adjacent and spaced from, respectively, said first andsecond boundary members.
 18. The method of claim 17 further comprisingfirst and second gas plenums, respectively, between said first gasinfeed conduit and said first infeed gas diffuser, and between saidsecond gas infeed conduit and said second infeed gas diffuser.
 19. Theapparatus of claim 18 further comprising first and second gas manifoldsmounted respectively, adjacent and between said first end of said secondconduit and said first boundary member, and adjacent and between saidsecond end of said second conduit and said second boundary member. 20.The method of claim 11 further comprising: a) providing a means fordetecting a drawing of said oxygen enriched gas to said end use fromsaid second conduit, a means for detecting a pressure drop below a lowerthreshold pressure in a reservoir of said oxygen enriched gascooperating in fluid communication with said second conduit wherein saidpressure drop is due to said drawing of said oxygen enriched gas fromsaid second conduit, a means for signalling said pressure drop to saidmeans for controlling gas flow; b) establishing a pressurized reservoirof said oxygen enriched gas for delivery through said second conduit forsaid end use; c) ceasing said flow of gas into or between said first andsecond chambers once said pressurized reservoir of said oxygen enrichedgas is established until said pressure drop below said lower thresholdpressure, upon the detection of which re-commencing said flow of gasinto or between said first and second chambers.
 21. The method of claim20 further comprising providing a discrete reservoir for said reservoirof said oxygen enriched gas.
 22. The method of claim 20 wherein saidproduct ends provide said reservoir of said oxygen enriched gas.
 23. Themethod of claim 20 further comprising the step of monitoring pressure insaid reservoir of said oxygen enriched gas.
 24. The method of claim 23further comprising the step of ceasing production of said oxygenenriched gas upon detection of pressure equal to or greater than anupper threshold pressure in said reservoir of said oxygen enriched gas.25. The method of claim 24 further comprising providing a means forselectively varying a delivery volume of said oxygen enriched gasdelivered per said drawing to said end use.
 26. The method of claim 25further comprising providing a means for selectively varying thesensitivity of said means for detecting a drawing of said oxygenenriched gas.
 27. The method of claim 26 further comprising the stepsof: a) pre-setting a selectively adjustable oxygen conservation ratio insaid means for controlling gas flow and a selectively adjustable drawingsensitivity, b) monitoring for pressure change which, according to saiddrawing sensitivity, is indicative of drawing of said oxygen enrichedgas from said second conduit for said end use, c) upon detection of saidsharp pressure change, allowing said oxygen enriched gas to flow fromsaid reservoir along said second conduit to said end use in a volumeaccording to said pre-set oxygen conservation ratio.
 28. The method ofclaim 27 comprising the further steps of: a) monitoring time intervalsbetween or frequency of sequential said drawings of said oxygen enrichedgas, b) selectively varying said conservation ratio and/or said drawingsensitivity so as to: (i) increase said sensitivity upon an increase insaid time interval or drop in said frequency relative to first thresholdvalues; (ii) decrease said sensitivity upon a decrease in said timeinterval or increase in said frequency relative to second thresholdvalues; (iii) increase said conservation ratio so as to decrease supplyof said oxygen enriched gas if said conservation ratio is low and saiddrawing frequency is low; or, (iv) decrease said conservation ratio soas to increase supply of said oxygen enriched gas if said conservationratio is high and said drawing frequency is high.
 29. In a pressureswing adsorption (PSA) process wherein a gaseous feedstock mixture of aless strongly adsorbed component in admixture with a more stronglyadsorbed component is separated from said feedstock in a reactor havinga bed of particulate adsorbent, the improvement comprising the steps of:(a) passing said feedstock into said reactor; (b) fitting said reactorwith a gas diffuser plate to create a initial adsorption zone filledwith said particulate adsorbent bed and a subsequent void zone fromwhich said less strongly adsorbed component is withdrawn; (c)determining the ratio of said void zone to said adsorption zone based onthe relative percentages of the gasses in said feedstock and the bulkloading factor of said particulate adsorbent; and (d) locating saiddiffuser plate based on said determined ratio.
 30. The process of claim29, wherein said feedstock comprises air, said less strongly adsorbedcomponent comprises oxygen, said more strongly adsorbed componentcomprises nitrogen, said particulate adsorbent comprises a zeolite, saidbulk loading factor is substantially 3:1.
 31. The process of claim 29,wherein said reactor is pressurized with said feedstock.